Uninterruptible power systems particularly in communication systems often utilize photovoltaic systems, thermoelectric generators (TEG) or organic Rankine cycle energy converters. A diesel engine based uninterruptible power sources (UPS) utilizes batteries or a flywheel to supply an electrical load when line power drops out and until the diesel can start and bring the generator on line.
In telecommunications systems, redundant organic Rankine cycle energy converters each operating at partial load have been used so that, failure of one converter causes the other converter to supply the full load. A transient period, until which the second energy converter delivers the full load, which can last from a few minutes up to about 20-50 minutes can be reduced by a standard battery that delivers a few ampere-hours.
Since 1976, as part of the Trans-Alaska Pipeline Project, a large number of stations have been operating each using a single Organic Rankine cycle turbine unit as a warm standby unit to ensure the required reliability. In such a standby unit, a line-operated electric heater under themostatic control provides external heat to a vapor generator of the unit to maintain the working fluid at about 120° F. When power fails, the main burner is activated quickly bringing the organic vapor Rankine cycle turbine unit on line delivering full power to the station as described in Trans-Alaska Pipeline, Remote Gate Valve Equipment Buildings, Operation and Maintenance Manual, Volume II, Ormat Energy Converter Model 155, April 1976).
In a related system disclosed in U.S. Pat. No. 4,982,569, the disclosure of which is hereby incorporated by reference, a hybrid power system is disclosed that includes an intermittently operable non-fuel consuming power generator, such as a photovoltaic cell array, or a wind generator, connected through a control-circuit to a battery for changing the same and for supplying current to a time-wise, substantially constant, electrical load. In addition, this hybrid power plant includes an electric generator connected to an intermittently operable prime mover, such as a Rankine cycle organic vapor turbogenerator for charging the battery and supplying current to the electrical load when the prime mover is operated, and a sensor for sensing at least one electrical parameter of the power plant. With such an arrangement, the prime mover is operable only when the power generator is not operating.
In another related system disclosed in U.S. Pat. No. 4,760,705, the disclosure of which is hereby incorporated by reference, the invention disclosed therein relates to a Rankine cycle power plant operating with an improved working fluid, the working fluid being a compound selected from the group consisting of bicyclic aromatic hydrocarbons, substituted bicyclic aromatic hydrocarbons, heterocyclic aromatic hydrocarbons, substituted heterocyclic aromatic hydrocarbons, bicyclic or heterobicyclic compounds where one ring is aromatic and the other condensed ring in a non-aromatic, and their mixtures. In a further aspect of the invention disclosed in this U.S. patent, a binary Rankine cycle power plant is provided in which the condenser of the high temperature and pressure turbine is cooled by a different working fluid which is vaporized thereby and supplied to a low temperature and pressure turbine.
Israel Patent 43547 discloses a further related system and discloses a rotor for a homopolar electrical machine.
Batteries are used in all the telecommunication projects to provide DC power to the telecom equipment and the reliability and availability of the system depends strongly on the battery characteristics.
The batteries have a limited lifetime and if not properly charged and maintained they have to be replaced a few times during the life of a project estimated as 20-25 years.
In addition, because the battery condition cannot be correctly assessed, battery failure occurs without any kind of advance notice, station shut-down often occurs unexpectedly. Moreover, the battery fails when they are actually needed so that, when there is an electrical grid power outage, the diesel generator fails when it is attempted to start it consequently causes the battery, UPS and diesel generator not to provide power.
It is therefore an object of the present invention to provide a new and improved method of and apparatus for providing uninterruptible power wherein the disadvantages as outlined are reduced or substantially overcome.